1. Field of the Invention
The present invention relates to a setting tool for setting pin-shaped elements and including means for controlling the setting depth, and to a method of controlling the setting depth.
2. Description of the Prior Art
With conventional setting tools of the type discussed above, a drive piston, which is accelerated usually as a result of an explosion of an explosive powder charge cartridge or combustion of a gas mixture in a combustion chamber of the tool, drives, e.g., a pin-shaped nail in a constructional component.
The pin-shaped nail is driven in the constructional component as a result of application of the motion energy of the drive piston thereto. The motion energy is determined by the hardness of the constructional component into which the nail is to be driven, and by the desired setting depth. The required motion energy is obtained by selecting an appropriate explosive powder cartridge or a gas mixture composition, by choosing an appropriate combustion chamber volume, an initial position of the drive piston and corresponding damping means. Usually, preliminary tests are conducted in order to determine a necessary time period and consumption of the material.
German Publication DE-3930592A1 discloses an explosive powder charge-operated setting tool having a drive piston and elastic damping elements which permit to control the setting depth. In the known setting tool, the setting depth for a following nail is adjusted by manually adjusting the initial position of the drive piston relative to the corresponding damping elements.
European Publication EP-338257B1 discloses a percussion tool with an electronic control of the impact energy for following each other impacts applied to the same nail. The impact energy of a following impact applied to the same nail is determined in accordance with a stored control function for a current conduction angle of the electromagnetic percussion mechanism and in accordance with a change of a penetration depth resulting from application of a previous impact. The change of the penetration depth is determined with an optical or magnetic incremental position sensor that determines a position of the electromagnetically driven drive piston with reference to the position of the lower dead point of the drive piston movement. After the predetermined set value of the setting depth is reached, which is determined by addition of changes of penetration depths caused by separate impacts or by an end position sensor, the drive-in process ends, and the impact energy control for a following drive-in process is initiated. The foregoing impact energy control of separate impacts applied to the same nail cannot be used in setting tool with a single drive-in impact or step.
Accordingly, an object of the present invention is to provide a setting tool with a setting depth control for a single drive-in step.
Another object of the present invention is to provide a method of controlling a setting depth in single drive-in step setting tools.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing an explosive powder charge-operated setting tool including a drive piston, which is driven by an expandable, in a combustion chamber, propellant, for driving a pin-shaped nail in a constructional component in a single drive-in step, and a control circuit for controlling a setting depth and having control electronics, a set point generator for setting the setting depth, a position sensor for determining a position of a lower dead point of the movement of the drive piston, and a regulator for an automatic adjustment of a motion energy of the drive piston; and by providing a method of controlling the setting depth and including:
initiating a drive-in process;
numerically determining a position of the drive piston during the drive-in process with the position sensor, and determining a position of a lower dead point of the movement of the drive piston in response to signals generated by the position-determining sensor;
generating, based on the position of the lower dead point and a set value of the setting depth, a control variable for a following drive-in process;
temporary storing the control variable as a setup variable for a following drive-in process;
adjusting the motion energy of the drive piston with the regulator in accordance with the temporary stored setup or control variable; and
effecting the following drive-in process.
During the following drive-in steps, the above-described four steps are periodically repeated, whereby in the second drive-in step, an automatic regulation takes place.
In accordance with the setting depth of the last driven-in nail, which is determined with the position sensor, the control electronics determines the motion energy for the following drive-in step for driving-in of the next nail. The motion energy value is temporary stored by the motion energy regulator. Thereby, a setting depth, which was achieved in a single drive-in step in accordance with a predetermined set value, is reached in several following each other steps.
Advantageously, the regulator is formed as an electrically controlled mechanical actuator which also controls in per se known manner the amount of propellant, mixing ratio, combustion chamber volume, propellant drain means, and/or the position of the damping means.
Advantageously, the position sensor is formed as an incremental sensor for sensing of a plurality of axially equidistant, advantageously, rotationally symmetrical marks provided on the drive piston. Advantageously, the position sensor is associated with a counter integrated in control electronics, whereby a small and robust construction of the position sensor is obtained.
Advantageously, the incremental sensor is formed as a magnetic field-sensing semiconductor sensor, such as a magneto-resistance sensor or as a Hall-sensor, for sensing sensor mark-forming projections and depressions which are provided on the drive piston and which modulate a permanent magnetic field generated at a location of the semiconductor sensor, advantageously, by a permanent magnet.
Advantageously, the sensor marks are formed as small residual webs provided between respective two closely adjacent annular grooves. The sharp curvature of the surfaces of the projecting webs insures that the measured variable, which is determined by the change of the magnetic field, is sufficiently large. On the other hand, the fatigue notch factor of the annular groove for the remaining cross-section of the drive piston, which is subjected to high mechanical alternating stresses, is rather small.
Advantageously, the incremental sensor is formed of at least two sensor elements which are connected with each other in antiphase for measuring differential measurement value data.
The formation of the sensor in above-described manner permits to practically eliminate fluctuations of absolute measurement values which can result from a radial backlash of set pins in their guide and that can reach up to 0.6 mm.
Advantageously, the two sensor elements are axially offset relative to each other by a one-fourth (xc2xc) of a distance between two adjacent sensor marks. This permits to determine, over the time rank, a change of the measurement value registered in both sensor elements by using quadrature detection of the direction of the axial movement of the nail. Whereby, the lower dead point of the drive piston movement, in particular, can be reliably determined upon change of the direction.
Advantageously, the position sensor is associated with a timer, which permits to reliably detect the lower dead point over the time maximum. In addition, in connection with the spacing between the sensor marks, the speed of the set nail, which is correlated with the setting energy, can be calculated. Also, the determination of the hardness of the constructional component by using the Windsor method becomes possible. This hardness as well as the setting depth can be displayed.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of the preferred embodiment, when read with reference to the accompanying drawings.